System and method for using impulse radio technology to track the movement of athletes and to enable secure communications between the athletes and their teammates, fans or coaches

ABSTRACT

A system, electronic device and method are provided that utilize the positioning capabilities of impulse radio technology to track one or more moving athletes. The movement of these athletes can be displayed on a television, a handheld unit or an Internet site. In addition, the present invention can utilize the communication capabilities of impulse radio technology to enable secure communications to take place between an athlete and their teammates, fans or coaches. The athletes can include, for example, track and field athletes, baseball players, football players, basketball players, soccer players or hockey players.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a system, electronic deviceand method capable of using impulse radio technology to track themovement of athletes and/or to enable secure communications to takeplace between the athletes and their teammates, fans or coaches.

2. Description of Related Art

In a sports environment, it would be desirable to have a system that cantrack the positions of athletes (e.g., football players, baseballplayers, soccer players, hockey players and the like) as they move on afield (e.g., football field, baseball diamond, soccer field, hockey rinkand the like) and at the same time with the same type of technologyenable secure communications to take place between these athletes andtheir teammates, fans or coaches. Unfortunately, to date there does notappear to be any tracking system that can effectively track the movementof one or more athletes on a field. In addition, to date there does notappear to be any communications system that can effectively enable oneor more athletes to communicate in a secure manner with their teammates,fans or coaches. As such, there does not appear to be any conventionalsystem that can track athletes and at the same time enable the athletesto communicate in a secure manner with their teammates, fans or coaches.Accordingly, there is a need for a system, electronic device and methodthat tracks a moving athlete and/or enables secure communications tooccur between an athlete and their teammates, fans or coaches. Theseneeds and other needs are satisfied by the present invention.

BRIEF DESCRIPTION OF THE INVENTION

The present invention includes a system, electronic device and methodthat utilizes the positioning capabilities of impulse radio technologyto track one or more moving athletes. The movement of these athletes canbe displayed on a television, a handheld unit or an Internet site. Inaddition, the present invention can utilize the communicationcapabilities of impulse radio technology to enable secure communicationsto take place between an athlete and their teammates, fans or coaches.The athletes can include, for example, track and field athletes,baseball players, football players, basketball players, soccer playersor hockey players.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be had byreference to the following detailed description when taken inconjunction with the accompanying drawings wherein:

FIG. 1A illustrates a representative Gaussian Monocycle waveform in thetime domain;

FIG. 1B illustrates the frequency domain amplitude of the GaussianMonocycle of FIG. 1A;

FIG. 1C represents the second derivative of the Gaussian Monocycle ofFIG. 1A;

FIG. 1D represents the third derivative of the Gaussian Monocycle ofFIG. 1A;

FIG. 1E represents the Correlator Output vs. the Relative Delay in areal data pulse;

FIG. 1F graphically depicts the frequency plot of the Gaussian family ofthe Gaussian Pulse and the first, second, and third derivative.

FIG. 2A illustrates a pulse train comprising pulses as in FIG. 1A;

FIG. 2B illustrates the frequency domain amplitude of the waveform ofFIG. 2A;

FIG. 2C illustrates the pulse train spectrum;

FIG. 2D is a plot of the Frequency vs. Energy Plot and points out thecoded signal energy spikes;

FIG. 3 illustrates the cross-correlation of two codes graphically asCoincidences vs. Time Offset;

FIGS. 4A-4E graphically illustrate five modulation techniques toinclude: Early-Late Modulation; One of Many Modulation; Flip Modulation;Quad Flip Modulation; and Vector Modulation;

FIG. 5A illustrates representative signals of an interfering signal, acoded received pulse train and a coded reference pulse train;

FIG. 5B depicts a typical geometrical configuration giving rise tomultipath received signals;

FIG. 5C illustrates exemplary multipath signals in the time domain;

FIGS. 5D-5F illustrate a signal plot of various multipath environments.

FIG. 5G illustrates the Rayleigh fading curve associated withnon-impulse radio transmissions in a multipath environment.

FIG. 5H illustrates a plurality of multipaths with a plurality ofreflectors from a transmitter to a receiver.

FIG. 5I graphically represents signal strength as volts vs. time in adirect path and multipath environment.

FIG. 6 illustrates a representative impulse radio transmitter functionaldiagram;

FIG. 7 illustrates a representative impulse radio receiver functionaldiagram;

FIG. 8A illustrates a representative received pulse signal at the inputto the correlator;

FIG. 8B illustrates a sequence of representative impulse signals in thecorrelation process;

FIG. 8C illustrates the output of the correlator for each of the timeoffsets of FIG. 8B.

FIG. 9 is a diagram illustrating the basic components of a system inaccordance with the present invention.

FIG. 10 is a diagram illustrating in greater detail an electronic deviceof the system shown in FIG. 9.

FIG. 11 is a diagram illustrating the system of FIG. 9 used on afootball field.

FIG. 12 is a flowchart illustrating the basic steps of a preferredmethod for tracking an athlete and/or for enabling communicationsbetween the athlete and their teammates, fans or coaches in accordancewith the present invention.

FIG. 13 is a block diagram of an impulse radio positioning networkutilizing a synchronized transceiver tracking architecture that can beused in the present invention.

FIG. 14 is a block diagram of an impulse radio positioning networkutilizing an unsynchronized transceiver tracking architecture that canbe used in the present invention.

FIG. 15 is a block diagram of an impulse radio positioning networkutilizing a synchronized transmitter tracking architecture that can beused in the present invention.

FIG. 16 is a block diagram of an impulse radio positioning networkutilizing an unsynchronized transmitter tracking architecture that canbe used in the present invention.

FIG. 17 is a block diagram of an impulse radio positioning networkutilizing a synchronized receiver tracking architecture that can be usedin the present invention.

FIG. 18 is a block diagram of an impulse radio positioning networkutilizing an unsynchronized receiver tracking architecture that can beused in the present invention.

FIG. 19 is a diagram of an impulse radio positioning network utilizing amixed mode reference radio tracking architecture that can be used in thepresent invention.

FIG. 20 is a diagram of an impulse radio positioning network utilizing amixed mode mobile electronic device tracking architecture that can beused in the present invention.

FIG. 21 is a diagram of a steerable null antennae architecture capableof being used in an impulse radio positioning network in accordance thepresent invention.

FIG. 22 is a diagram of a specialized difference antennae architecturecapable of being used in an impulse radio positioning network inaccordance the present invention.

FIG. 23 is a diagram of a specialized directional antennae architecturecapable of being used in an impulse radio positioning network inaccordance with the present invention.

FIG. 24 is a diagram of an amplitude sensing architecture capable ofbeing used in an impulse radio positioning network in accordance withthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes a system, electronic device and methodcapable using impulse radio technology to track a moving athlete and/orenable secure communications to occur between an athlete and theirteammates, fans or coaches. This ability to track an athlete as theymove around a field and/or enable secure communications to occur betweenan athlete and their teammates, fans or coaches are significantimprovements over the state-of-art. These significant improvements overthe state-of-art are attributable, in part, to the use of the emergingand revolutionary ultra wideband technology (UWB) called impulse radiocommunication technology (also known as impulse radio).

Impulse radio has been described in a series of patents, including U.S.Pat. Nos. 4,641,317 (issued Feb. 3, 1987), 4,813,057 (issued Mar. 14,1989), 4,979,186 (issued Dec. 18, 1990) and 5,363,108 (issued Nov. 8,1994) to Larry W. Fullerton. A second generation of impulse radiopatents includes U.S. Pat. Nos. 5,677,927 (issued Oct. 14, 1997),5,687,169 (issued Nov. 11, 1997), 5,764,696 (issued Jun. 9, 1998), and5,832,035 (issued Nov. 3, 1998) to Fullerton et al.

Uses of impulse radio systems are described in U.S. patent applicationSer. No. 09/332,502, titled, “System and Method for Intrusion Detectionusing a Time Domain Radar Array” and U.S. patent application Ser. No.09/332,503, titled, “Wide Area Time Domain Radar Array” both filed onJun. 14, 1999 both of which are assigned to the assignee of the presentinvention. The above patent documents are incorporated herein byreference.

This section provides an overview of impulse radio technology andrelevant aspects of communications theory. It is provided to assist thereader with understanding the present invention and should not be usedto limit the scope of the present invention. It should be understoodthat the terminology ‘impulse radio’ is used primarily for historicalconvenience and that the terminology can be generally interchanged withthe terminology ‘impulse communications system, ultra-wideband system,or ultra-wideband communication systems’. Furthermore, it should beunderstood that the described impulse radio technology is generallyapplicable to various other impulse system applications including butnot limited to impulse radar systems and impulse positioning systems.Accordingly, the terminology ‘impulse radio’ can be generallyinterchanged with the terminology ‘impulse transmission system andimpulse reception system.’

Impulse radio refers to a radio system based on short, low duty-cyclepulses. An ideal impulse radio waveform is a short Gaussian monocycle.As the name suggests, this waveform attempts to approach one cycle ofradio frequency (RF) energy at a desired center frequency. Due toimplementation and other spectral limitations, this waveform may bealtered significantly in practice for a given application. Manywaveforms having very broad, or wide, spectral bandwidth approximate aGaussian shape to a useful degree.

Impulse radio can use many types of modulation, including amplitudemodulation, phase modulation, frequency modulation, time-shiftmodulation (also referred to as pulse-position modulation orpulse-interval modulation) and M-ary versions of these. In thisdocument, the time-shift modulation method is often used as anillustrative example. However, someone skilled in the art will recognizethat alternative modulation approaches may, in some instances, be usedinstead of or in combination with the time-shift modulation approach.

In impulse radio communications, inter-pulse spacing may be heldconstant or may be varied on a pulse-by-pulse basis by information, acode, or both. Generally, conventional spread spectrum systems employcodes to spread the normally narrow band information signal over arelatively wide band of frequencies. A conventional spread spectrumreceiver correlates these signals to retrieve the original informationsignal. In impulse radio communications, codes are not typically usedfor energy spreading because the monocycle pulses themselves have aninherently wide bandwidth. Codes are more commonly used forchannelization, energy smoothing in the frequency domain, resistance tointerference, and reducing the interference potential to nearbyreceivers. Such codes are commonly referred to as time-hopping codes orpseudo-noise (PN) codes since their use typically causes inter-pulsespacing to have a seemingly random nature. PN codes may be generated bytechniques other than pseudorandom code generation. Additionally, pulsetrains having constant, or uniform, pulse spacing are commonly referredto as uncoded pulse trains. A pulse train with uniform pulse spacing,however, may be described by a code that specifies non-temporal, i.e.,non-time related, pulse characteristics.

In impulse radio communications utilizing time-shift modulation,information comprising one or more bits of data typically time-positionmodulates a sequence of pulses. This yields a modulated, coded timingsignal that comprises a train of pulses from which a typical impulseradio receiver employing the same code may demodulate and, if necessary,coherently integrate pulses to recover the transmitted information.

The impulse radio receiver is typically a direct conversion receiverwith a cross correlator front-end that coherently converts anelectromagnetic pulse train of monocycle pulses to a baseband signal ina single stage. The baseband signal is the basic information signal forthe impulse radio communications system. A subcarrier may also beincluded with the baseband signal to reduce the effects of amplifierdrift and low frequency noise. Typically, the subcarrier alternatelyreverses modulation according to a known pattern at a rate faster thanthe data rate. This same pattern is used to reverse the process andrestore the original data pattern just before detection. This methodpermits alternating current (AC) coupling of stages, or equivalentsignal processing, to eliminate direct current (DC) drift and errorsfrom the detection process. This method is described in more detail inU.S. Pat. No. 5,677,927 to Fullerton et al.

Waveforms

Impulse transmission systems are based on short, low duty-cycle pulses.Different pulse waveforms, or pulse types, may be employed toaccommodate requirements of various applications. Typical pulse typesinclude a Gaussian pulse, pulse doublet (also referred to as a Gaussianmonocycle), pulse triplet, and pulse quadlet as depicted in FIGS. 1Athrough 1D, respectively. An actual received waveform that closelyresembles the theoretical pulse quadlet is shown in FIG. 1E. A pulsetype may also be a wavelet set produced by combining two or more pulsewaveforms (e.g., a doublet/triplet wavelet set). These different pulsetypes may be produced by methods described in the patent documentsreferenced above or by other methods, as persons skilled in the artwould understand.

For analysis purposes, it is convenient to model pulse waveforms in anideal manner. For example, the transmitted waveform produced bysupplying a step function into an ultra-wideband antenna may be modeledas a Gaussian monocycle. A Gaussian monocycle (normalized to a peakvalue of 1) may be described by:${f_{mono}(t)} = {\sqrt{e}\left( \frac{t}{\sigma} \right)e^{\frac{- t^{2}}{2\sigma^{2}}}}$

where σ is a time scaling parameter, t is time, and e is the naturallogarithm base.

The power special density of the Gaussian monocycle is shown in FIG. 1F,along with spectrums for the Gaussian pulse, triplet, and quadlet. Thecorresponding equation for the Gaussian monocycle is:${F_{mono}(f)} = {\left( {2\pi} \right)^{\frac{3}{2}}\sigma \quad f\quad e^{{- 2}{({{\pi\sigma}\quad f})}^{2}}}$

The center frequency (f_(c)), or frequency of peak spectral density, ofthe Gaussian monocycle is: $f_{c} = \frac{1}{2{\pi\sigma}}$

It should be noted that the output of an ultra-wideband antenna isessentially equal to the derivative of its input. Accordingly, since thepulse doublet, pulse triplet, and pulse quadlet are the first, second,and third derivatives of the Gaussian pulse, in an ideal model, anantenna receiving a Gaussian pulse will transmit a Gaussian monocycleand an antenna receiving a Gaussian monocycle will provide a pulsetriplet.

Pulse Trains

Impulse transmission systems may communicate one or more data bits witha single pulse; however, typically each data bit is communicated using asequence of pulses, known as a pulse train. As described in detail inthe following example system, the impulse radio transmitter produces andoutputs a train of pulses for each bit of information. FIGS. 2A and 2Bare illustrations of the output of a typical 10 megapulses per second(Mpps) system with uncoded, unmodulated pulses, each having a width of0.5 nanoseconds (ns). FIG. 2A shows a time domain representation of thepulse train output. FIG. 2B illustrates that the result of the pulsetrain in the frequency domain is to produce a spectrum comprising a setof comb lines spaced at the frequency of the 10 Mpps pulse repetitionrate. When the full spectrum is shown, as in FIG. 2C, the envelope ofthe comb line spectrum corresponds to the curve of the single Gaussianmonocycle spectrum in FIG. 1F. For this simple uncoded case, the powerof the pulse train is spread among roughly two hundred comb lines. Eachcomb line thus has a small fraction of the total power and presents muchless of an interference problem to a receiver sharing the band. It canalso be observed from FIG. 2A that impulse transmission systemstypically have very low average duty cycles, resulting in average powerlower than peak power. The duty cycle of the signal in FIG. 2A is if0.5%, based on a 0.5 ns pulse duration in a 100 ns interval.

The signal of an uncoded, unmodulated pulse train may be expressed:${s(t)} = {\left( {- 1} \right)^{f}a{\sum\limits_{j}{\omega \left( {{{ct} - {jT}_{f}},b} \right)}}}$

where j is the index of a pulse within a pulse train, (−1)^(f) ispolarity (+/−), a is pulse amplitude, b is pulse type, c is pulse width,ω(t,b) is the normalized pulse waveform, and T_(f) is pulse repetitiontime.

The energy spectrum of a pulse train signal over a frequency bandwidthof interest may be determined by summing the phasors of the pulses ateach frequency, using the following equation:${A(\omega)} = {{\sum\limits_{i = 1}^{n}\frac{e^{j\quad \Delta \quad t}}{n}}}$

where A(ω) is the amplitude of the spectral response at a givenfrequency□□ω□ is the frequency being analyzed (2πf), Δt is the relativetime delay of each pulse from the start of time period, and n is thetotal number of pulses in the pulse train.

A pulse train can also be characterized by its autocorrelation andcross-correlation properties. Autocorrelation properties pertain to thenumber of pulse coincidences (i.e., simultaneous arrival of pulses) thatoccur when a pulse train is correlated against an instance of itselfthat is offset in time. Of primary importance is the ratio of the numberof pulses in the pulse train to the maximum number of coincidences thatoccur for any time offset across the period of the pulse train. Thisratio is commonly referred to as the main-lobe-to-side-lobe ratio, wherethe greater the ratio, the easier it is to acquire and field a signal.

Cross-correlation properties involve the potential for pulses from twodifferent signals simultaneously arriving, or coinciding, at a receiver.Of primary importance are the maximum and average numbers of pulsecoincidences that may occur between two pulse trains. As the number ofcoincidences increases, the propensity for data errors increases.Accordingly, pulse train cross-correlation properties are used indetermining channelization capabilities of impulse transmission systems(i.e., the ability to simultaneously operate within close proximity).

Coding

Specialized coding techniques can be employed to specify temporal and/ornon-temporal pulse characteristics to produce a pulse train havingcertain spectral and/or correlation properties. For example, byemploying a PN code to vary inter-pulse spacing, the energy in the comblines presented in FIG. 2B can be distributed to other frequencies asdepicted in FIG. 2D, thereby decreasing the peak spectral density withina bandwidth of interest. Note that the spectrum retains certainproperties that depend on the specific (temporal) PN code used. Spectralproperties can be similarly affected by using non-temporal coding (e.g.,inverting certain pulses).

Coding provides a method of establishing independent communicationchannels. Specifically, families of codes can be designed such that thenumber of pulse coincidences between pulse trains produced by any twocodes will be minimal. For example, FIG. 3 depicts cross-correlationproperties of two codes that have no more than four coincidences for anytime offset. Generally, keeping the number of pulse collisions minimalrepresents a substantial attenuation of the unwanted signal.

Coding can also be used to facilitate signal acquisition. For example,coding techniques can be used to produce pulse trains with a desirablemain-lobe-to-side-lobe ratio. In addition, coding can be used to reduceacquisition algorithm search space.

Coding methods for specifying temporal and non-temporal pulsecharacteristics are described in commonly owned, co-pending applicationstitled “A Method and Apparatus for Positioning Pulses in Time,”application Ser. No. 09/592,249, and “A Method for SpecifyingNon-Temporal Pulse Characteristics,” application Ser. No. 09/592,250,both filed Jun. 12, 2000, and both of which are incorporated herein byreference.

Typically, a code consists of a number of code elements having integeror floating-point values. A code element value may specify a singlepulse characteristic or may be subdivided into multiple components, eachspecifying a different pulse characteristic. Code element or codecomponent values typically map to a pulse characteristic value layoutthat may be fixed or non-fixed and may involve value ranges, discretevalues, or a combination of value ranges and discrete values. A valuerange layout specifies a range of values that is divided into componentsthat are each subdivided into subcomponents, which can be furthersubdivided, as desired. In contrast, a discrete value layout involvesuniformly or non-uniformly distributed discrete values. A non-fixedlayout (also referred to as a delta layout) involves delta valuesrelative to some reference value. Fixed and non-fixed layouts, andapproaches for mapping code element/component values, are described inco-owned, co-pending applications, titled “Method for Specifying PulseCharacteristics using Codes,” application Ser. No. 09/592,290 and “AMethod and Apparatus for Mapping Pulses to a Non-Fixed Layout,”application Ser. No. 09/591,691, both filed on Jun. 12, 2000, both ofwhich are incorporated herein by reference.

A fixed or non-fixed characteristic value layout may include anon-allowable region within which a pulse characteristic value isdisallowed. A method for specifying non-allowable regions is describedin co-owned, co-pending application titled “A Method for SpecifyingNon-Allowable Pulse Characteristics,” application Ser. No. 09/592,289,filed Jun. 12, 2000, and incorporated herein by reference. A relatedmethod that conditionally positions pulses depending on whether codeelements map to non-allowable regions is described in co-owned,co-pending application, titled “A Method and Apparatus for PositioningPulses Using a Layout having Non-Allowable Regions,” application Ser.No. 09/592,248 filed Jun. 12, 2000, and incorporated herein byreference.

The signal of a coded pulse train can be generally expressed by:${s_{tr}^{(k)}*(t)} = {\sum\limits_{j}{\left( {- 1} \right)^{f_{j}^{(k)}}a_{j}^{(k)}{\omega \left( {{{c_{j}^{(k)}t} - T_{j}^{(k)}},b_{j}^{(k)}} \right)}}}$

where k is the index of a transmitter, j is the index of a pulse withinits pulse train, (−1)f_(j) ^((k)), a_(j) ^((k)), b_(j) ^((k)), c_(j)^((k)), and ω(t,b_(j) ^((k))) are the coded polarity, pulse amplitude,pulse type, pulse width, and normalized pulse waveform of the jth pulseof the kth transmitter, and T_(j) ^((k)) is the coded time shift of thejth pulse of the kth transmitter. Note: When a given non-temporalcharacteristic does not vary (i.e., remains constant for all pulses), itbecomes a constant in front of the summation sign.

Various numerical code generation methods can be employed to producecodes having certain correlation and spectral properties. Such codestypically fall into one of two categories: designed codes andpseudorandom codes. A designed code may be generated using a quadraticcongruential, hyperbolic congruential, linear congruential, Costasarray, or other such numerical code generation technique designed togenerate codes having certain correlation properties. A pseudorandomcode may be generated using a computer's random number generator, binaryshift-register(s) mapped to binary words, a chaotic code generationscheme, or the like. Such ‘random-like’ codes are attractive for certainapplications since they tend to spread spectral energy over multiplefrequencies while having ‘good enough’ correlation properties, whereasdesigned codes may have superior correlation properties but possess lesssuitable spectral properties. Detailed descriptions of numerical codegeneration techniques are included in a co-owned, co-pending patentapplication titled “A Method and Apparatus for Positioning Pulses inTime,” application Ser. No. 09/592,248, filed Jun. 12, 2000, andincorporated herein by reference.

It may be necessary to apply predefined criteria to determine whether agenerated code, code family, or a subset of a code is acceptable for usewith a given UWB application. Criteria may include correlationproperties, spectral properties, code length, non-allowable regions,number of code family members, or other pulse characteristics. A methodfor applying predefined criteria to codes is described in co-owned,co-pending application, titled “A Method and Apparatus for SpecifyingPulse Characteristics using a Code that Satisfies Predefined Criteria,”application Ser. No. 09/592,288, filed Jun. 12, 2000, and incorporatedherein by reference.

In some applications, it may be desirable to employ a combination ofcodes. Codes may be combined sequentially, nested, or sequentiallynested, and code combinations may be repeated. Sequential codecombinations typically involve switching from one code to the next afterthe occurrence of some event and may also be used to support multicastcommunications. Nested code combinations may be employed to producepulse trains having desirable correlation and spectral properties. Forexample, a designed code may be used to specify value range componentswithin a layout and a nested pseudorandom code may be used to randomlyposition pulses within the value range components. With this approach,correlation properties of the designed code are maintained since thepulse positions specified by the nested code reside within the valuerange components specified by the designed code, while the randompositioning of the pulses within the components results in particularspectral properties. A method for applying code combinations isdescribed in co-owned, co-pending application, titled “Method andApparatus for Applying Codes Having Pre-Defined Properties,” applicationSer. No. 09/591,690, filed Jun. 12, 2000, and incorporated herein byreference.

Modulation

Various aspects of a pulse waveform may be modulated to conveyinformation and to further minimize structure in the resulting spectrum.Amplitude modulation, phase modulation, frequency modulation, time-shiftmodulation and M-ary versions of these were proposed in U.S. Pat. No.5,677,927 to Fullerton et al., previously incorporated by reference.Time-shift modulation can be described as shifting the position of apulse either forward or backward in time relative to a nominal coded (oruncoded) time position in response to an information signal. Thus, eachpulse in a train of pulses is typically delayed a different amount fromits respective time base clock position by an individual code delayamount plus a modulation time shift. This modulation time shift isnormally very small relative to the code shift. In a 10 Mpps system witha center frequency of 2 GHz, for example, the code may command pulseposition variations over a range of 100 ns, whereas, the informationmodulation may shift the pulse position by 150 ps. This two-state‘early-late’ form of time shift modulation is depicted in FIG. 4A.

A pulse train with conventional ‘early-late’ time-shift modulation canbe expressed:${s_{tr}^{(k)}(t)} = {\sum\limits_{j}{\left( {- 1} \right)^{f_{j}^{(k)}}a_{j}^{(k)}{\omega \left( {{{c_{j}^{(k)}t} - T_{j}^{(k)} - {\delta \quad d_{\lbrack{j/N_{s}}\rbrack}^{(k)}}},b_{j}^{(k)}} \right)}}}$

where k is the index of a transmitter, j is the index of a pulse withinits pulse train, (−1)f_(j) ^((k)), a_(j) ^((k)), b_(j) ^((k)), c_(j)^((k)), and ω(t,b_(j) ^((k))) are the coded polarity, pulse amplitude,pulse type, pulse width, and normalized pulse waveform of the jth pulseof the kth transmitter, T_(j) ^((k)) is the coded time shift of the jthpulse of the kth transmitter, d is the time shift added when thetransmitted symbol is 1 (instead of 0), d^((k)) is the data (i.e., 0or 1) transmitted by the kth transmitter, and N_(s) is the number ofpulses per symbol (e.g., bit). Similar expressions can be derived toaccommodate other proposed forms of modulation.

An alternative form of time-shift modulation can be described asOne-of-Many Position Modulation (OMPM). The OMPM approach, shown in FIG.4B, involves shifting a pulse to one of N possible modulation positionsabout a nominal coded (or uncoded) time position in response to aninformation signal, where N represents the number of possible states.For example, if N were four (4), two data bits of information could beconveyed. For further details regarding OMPM, see “Apparatus, System andMethod for One-of-Many Position Modulation in an Impulse RadioCommunication System,” U.S. patent application Ser. No. 09/875,290,filed Jun. 7, 2001, assigned to the assignee of the present invention,and incorporated herein by reference.

An impulse radio communications system can employ flip modulationtechniques to convey information. The simplest flip modulation techniqueinvolves transmission of a pulse or an inverted (or flipped) pulse torepresent a data bit of information, as depicted in FIG. 4C. Flipmodulation techniques may also be combined with time-shift modulationtechniques to create two, four, or more different data states. One suchflip with shift modulation technique is referred to as Quadrature FlipTime Modulation (QFTM). The QFTM approach is illustrated in FIG. 4D.Flip modulation techniques are further described in patent applicationtitled “Apparatus, System and Method for Flip Modulation in an ImpulseRadio Communication System,” application Ser. No. 09/537,692, filed Mar.29, 2000, assigned to the assignee of the present invention, andincorporated herein by reference.

Vector modulation techniques may also be used to convey information.Vector modulation includes the steps of generating and transmitting aseries of time-modulated pulses, each pulse delayed by one of at leastfour pre-determined time delay periods and representative of at leasttwo data bits of information, and receiving and demodulating the seriesof time-modulated pulses to estimate the data bits associated with eachpulse. Vector modulation is shown in FIG. 4E. Vector modulationtechniques are further described in patent application titled “VectorModulation System and Method for Wideband Impulse Radio Communications,”application Ser. No. 09/169,765, filed Dec. 9, 1999, assigned to theassignee of the present invention, and incorporated herein by reference.

Reception and Demodulation

Impulse radio systems operating within close proximity to each other maycause mutual interference. While coding minimizes mutual interference,the probability of pulse collisions increases as the number ofcoexisting impulse radio systems rises. Additionally, various othersignals may be present that cause interference. Impulse radios canoperate in the presence of mutual interference and other interferingsignals, in part because they do not depend on receiving everytransmitted pulse. Impulse radio receivers perform a correlating,synchronous receiving function (at the RF level) that uses statisticalsampling and combining, or integration, of many pulses to recovertransmitted information. Typically, 1 to 1000 or more pulses areintegrated to yield a single data bit thus diminishing the impact ofindividual pulse collisions, where the number of pulses that must beintegrated to successfully recover transmitted information depends on anumber of variables including pulse rate, bit rate, range andinterference levels.

Interference Resistance

Besides providing channelization and energy smoothing, coding makesimpulse radios highly resistant to interference by enablingdiscrimination between intended impulse transmissions and interferingtransmissions. This property is desirable since impulse radio systemsmust share the energy spectrum with conventional radio systems and withother impulse radio systems. FIG. 5A illustrates the result of a narrowband sinusoidal interference signal 502 overlaying an impulse radiosignal 504. At the impulse radio receiver, the input to the crosscorrelation would include the narrow band signal 502 and the receivedultrawide-band impulse radio signal 504. The input is sampled by thecross correlator using a template signal 506 positioned in accordancewith a code. Without coding, the cross correlation would sample theinterfering signal 502 with such regularity that the interfering signalscould cause interference to the impulse radio receiver. However, whenthe transmitted impulse signal is coded and the impulse radio receivertemplate signal 506 is synchronized using the identical code, thereceiver samples the interfering signals non-uniformly. The samples fromthe interfering signal add incoherently, increasing roughly according tothe square root of the number of samples integrated. The impulse radiosignal samples, however, add coherently, increasing directly accordingto the number of samples integrated. Thus, integrating over many pulsesovercomes the impact of interference.

Processing Gain

Impulse radio systems have exceptional processing gain due to their widespreading bandwidth. For typical spread spectrum systems, the definitionof processing gain, which quantifies the decrease in channelinterference when wide-band communications are used, is the ratio of thebandwidth of the channel to the bit rate of the information signal. Forexample, a direct sequence spread spectrum system with a 10 KHzinformation bandwidth and a 10 MHz channel bandwidth yields a processinggain of 1000, or 30 dB. However, far greater processing gains areachieved by impulse radio systems, where the same 10 KHz informationbandwidth is spread across a much greater 2 GHz channel bandwidth,resulting in a theoretical processing gain of 200,000, or 53 dB.

Capacity

It can be shown theoretically, using signal-to-noise arguments, thatthousands of simultaneous channels are available to an impulse radiosystem as a result of its exceptional processing gain.

The average output signal-to-noise ratio of the impulse radio may becalculated for randomly selected time-hopping codes as a function of thenumber of active users, N_(u), as:${{SNR}_{out}\left( N_{u} \right)} = \frac{\left( {N_{s}A_{1}m_{p}} \right)^{2}}{\sigma_{rec}^{2} + {N_{s}\sigma_{a}^{2}{\sum\limits_{k = 2}^{N_{u}}A_{k}^{2}}}}$

where N_(s) is the number of pulses integrated per bit of information,A_(k) models the attenuation of transmitter k's signal over thepropagation path to the receiver, and σ_(rec) ² is the variance of thereceiver noise component at the pulse train integrator output. Themonocycle waveform-dependent parameters m_(p) and σ_(a) ² are given bym_(p) = ∫_(−∞)^(∞)ω(t)[ω(t) − ω(t − δ)]t

and σ_(a)² = T_(f)⁻¹∫_(−∞)^(∞)[∫_(−∞)^(∞)ω(t − s)υ(t)t]²s,

where ?(t) is the monocycle waveform, ?(t)=?(t)−?(t−d) is the templatesignal waveform, d is the time shift between the monocycle waveform andthe template signal waveform, T_(f) is the pulse repetition time, and sis signal.

Multipath and Propagation

One of the advantages of impulse radio is its resistance to multipathfading effects. Conventional narrow band systems are subject tomultipath through the Rayleigh fading process, where the signals frommany delayed reflections combine at the receiver antenna according totheir seemingly random relative phases resulting in possible summationor possible cancellation, depending on the specific propagation to agiven location. Multipath fading effects are most adverse where a directpath signal is weak relative to multipath signals, which represents themajority of the potential coverage area of a radio system. In a mobilesystem, received signal strength fluctuates due to the changing mix ofmultipath signals that vary as its position varies relative to fixedtransmitters, mobile transmitters and signal-reflecting surfaces in theenvironment.

Impulse radios, however, can be substantially resistant to multipatheffects. Impulses arriving from delayed multipath reflections typicallyarrive outside of the correlation time and, thus, may be ignored. Thisprocess is described in detail with reference to FIGS. 5B and 5C. FIG.5B illustrates a typical multipath situation, such as in a building,where there are many reflectors 504B, 505B. In this figure, atransmitter 506B transmits a signal that propagates along three paths,the direct path 501B, path 1 502B, and path2 503B, to a receiver 508B,where the multiple reflected signals are combined at the antenna. Thedirect path 501B, representing the straight-line distance between thetransmitter and receiver, is the shortest. Path 1 502B represents amultipath reflection with a distance very close to that of the directpath. Path 2 503B represents a multipath reflection with a much longerdistance. Also shown are elliptical (or, in space, ellipsoidal) tracesthat represent other possible locations for reflectors that wouldproduce paths having the same distance and thus the same time delay.

FIG. 5C illustrates the received composite pulse waveform resulting fromthe three propagation paths 501B, 502B, and 503B shown in FIG. 5B. Inthis figure, the direct path signal 501B is shown as the first pulsesignal received. The path 1 and path 2 signals 502B, 503B comprise theremaining multipath signals, or multipath response, as illustrated. Thedirect path signal is the reference signal and represents the shortestpropagation time. The path 1 signal is delayed slightly and overlaps andenhances the signal strength at this delay value. The path 2 signal isdelayed sufficiently that the waveform is completely separated from thedirect path signal. Note that the reflected waves are reversed inpolarity. If the correlator template signal is positioned such that itwill sample the direct path signal, the path 2 signal will not besampled and thus will produce no response. However, it can be seen thatthe path 1 signal has an effect on the reception of the direct pathsignal since a portion of it would also be sampled by the templatesignal. Generally, multipath signals delayed less than one quarter wave(one quarter wave is about 1.5 inches, or 3.5 cm at 2 GHz centerfrequency) may attenuate the direct path signal. This region isequivalent to the first Fresnel zone in narrow band systems. Impulseradio, however, has no further nulls in the higher Fresnel zones. Thisability to avoid the highly variable attenuation from multipath givesimpulse radio significant performance advantages.

FIGS. 5D, 5E, and 5F represent the received signal from a TM-UWBtransmitter in three different multipath environments. These figures areapproximations of typical signal plots. FIG. 5D illustrates the receivedsignal in a very low multipath environment. This may occur in a buildingwhere the receiver antenna is in the middle of a room and is arelatively short, distance, for example, one meter, from thetransmitter. This may also represent signals received from a largerdistance, such as 100 meters, in an open field where there are noobjects to produce reflections. In this situation, the predominant pulseis the first received pulse and the multipath reflections are too weakto be significant. FIG. 5E illustrates an intermediate multipathenvironment. This approximates the response from one room to the next ina building. The amplitude of the direct path signal is less than in FIG.5D and several reflected signals are of significant amplitude. FIG. 5Fapproximates the response in a severe multipath environment such aspropagation through many rooms, from corner to corner in a building,within a metal cargo hold of a ship, within a metal truck trailer, orwithin an intermodal shipping container. In this scenario, the main pathsignal is weaker than in FIG. 5E. In this situation, the direct pathsignal power is small relative to the total signal power from thereflections.

An impulse radio receiver can receive the signal and demodulate theinformation using either the direct path signal or any multipath signalpeak having sufficient signal-to-noise ratio. Thus, the impulse radioreceiver can select the strongest response from among the many arrivingsignals. In order for the multipath signals to cancel and produce a nullat a given location, dozens of reflections would have to be cancelledsimultaneously and precisely while blocking the direct path, which is ahighly unlikely scenario. This time separation of mulitipath signalstogether with time resolution and selection by the receiver permit atype of time diversity that virtually eliminates cancellation of thesignal. In a multiple correlator rake receiver, performance is furtherimproved by collecting the signal power from multiple signal peaks foradditional signal-to-noise performance.

Where the system of FIG. 5B is a narrow band system and the delays aresmall relative to the data bit time, the received signal is a sum of alarge number of sine waves of random amplitude and phase. In theidealized limit, the resulting envelope amplitude has been shown tofollow a Rayleigh probability distribution as follows:${p(r)} = {\frac{r}{\sigma^{2}}{\exp \left( \frac{- r^{2}}{2\sigma^{2}} \right)}}$

where r is the envelope amplitude of the combined multipath signals, ands(2)½is the RMS power of the combined multipath signals. The Rayleighdistribution curve in FIG. 5G shows that 10% of the time, the signal ismore than 10 dB attenuated. This suggests that 10 dB fade margin isneeded to provide 90% link availability. Values of fade margin from 10to 40 dB have been suggested for various narrow band systems, dependingon the required reliability. This characteristic has been the subject ofmuch research and can be partially improved by such techniques asantenna and frequency diversity, but these techniques result inadditional complexity and cost.

In a high multipath environment such as inside homes, offices,warehouses, automobiles, trailers, shipping containers, or outside in anurban canyon or other situations where the propagation is such that thereceived signal is primarily scattered energy, impulse radio systems canavoid the Rayleigh fading mechanism that limits performance of narrowband systems, as illustrated in FIGS. 5H and 5I. FIG. 5H depicts animpulse radio system in a high multipath environment 500H consisting ofa transmitter 506H and a receiver 508H. A transmitted signal follows adirect path 501H and reflects off reflectors 503H via multiple paths502H. FIG. 5I illustrates the combined signal received by the receiver508H over time with the vertical axis being signal strength in volts andthe horizontal axis representing time in nanoseconds. The direct path501H results in the direct path signal 502I while the multiple paths502H result in multipath signals 504I. In the same manner describedearlier for FIGS. 5B and 5C, the direct path signal 502I is sampled,while the multipath signals 504I are not, resulting in Rayleigh fadingavoidance.

Distance Measurement and Positioning

Impulse systems can measure distances to relatively fine resolutionbecause of the absence of ambiguous cycles in the received waveform.Narrow band systems, on the other hand, are limited to the modulationenvelope and cannot easily distinguish precisely which RF cycle isassociated with each data bit because the cycle-to-cycle amplitudedifferences are so small they are masked by link or system noise. Sincean impulse radio waveform has no multi-cycle ambiguity, it is possibleto determine waveform position to less than a wavelength, potentiallydown to the noise floor of the system. This time position measurementcan be used to measure propagation delay to determine link distance to ahigh degree of precision. For example, 30 ps of time transfer resolutioncorresponds to approximately centimeter distance resolution. See, forexample, U.S. Pat. No. 6,133,876, issued Oct. 17, 2000, titled “Systemand Method for Position Determination by Impulse Radio,” and U.S. Pat.No. 6,111,536, issued Aug. 29, 2000, titled “System and Method forDistance Measurement by Inphase and Quadrature Signals in a RadioSystem,” both of which are incorporated herein by reference.

In addition to the methods articulated above, impulse radio technologyalong with Time Division Multiple Access algorithms and Time Domainpacket radios can achieve geo-positioning capabilities in a radionetwork. This geo-positioning method is described in co-owned,co-pending application titled “System and Method for Person or ObjectPosition Location Utilizing Impulse Radio,” application Ser. No.09/456,409, filed Dec. 8, 1999, and incorporated herein by reference.

Power Control

Power control systems comprise a first transceiver that transmits animpulse radio signal to a second transceiver. A power control update iscalculated according to a performance measurement of the signal receivedat the second transceiver. The transmitter power of either transceiver,depending on the particular setup, is adjusted according to the powercontrol update. Various performance measurements are employed tocalculate a power control update, including bit error rate,signal-to-noise ratio, and received signal strength, used alone or incombination. Interference is thereby reduced, which may improveperformance where multiple impulse radios are operating in closeproximity and their transmissions interfere with one another. Reducingthe transmitter power of each radio to a level that producessatisfactory reception increases the total number of radios that canoperate in an area without saturation. Reducing transmitter power alsoincreases transceiver efficiency.

For greater elaboration of impulse radio power control, see patentapplication titled “System and Method for Impulse Radio Power Control,”application Ser. No. 09/332,501, filed Jun. 14, 1999, assigned to theassignee of the present invention, and incorporated herein by reference.

Mitigating Effects of Interference

A method for mitigating interference in impulse radio systems comprisesthe steps of conveying the message in packets, repeating conveyance ofselected packets to make up a repeat package, and conveying the repeatpackage a plurality of times at a repeat period greater than twice theperiod of occurrence of the interference. The communication may convey amessage from a proximate transmitter to a distal receiver, and receive amessage by a proximate receiver from a distal transmitter. In such asystem, the method comprises the steps of providing interferenceindications by the distal receiver to the proximate transmitter, usingthe interference indications to determine predicted noise periods, andoperating the proximate transmitter to convey the message according toat least one of the following: (1) avoiding conveying the message duringnoise periods, (2) conveying the message at a higher power during noiseperiods, (3) increasing error detection coding in the message duringnoise periods, (4) re-transmitting the message following noise periods,(5) avoiding conveying the message when interference is greater than afirst strength, (6) conveying the message at a higher power when theinterference is greater than a second strength, (7) increasing errordetection coding in the message when the interference is greater than athird strength, and (8) re-transmitting a portion of the message afterinterference has subsided to less than a predetermined strength.

For greater elaboration of mitigating interference in impulse radiosystems, see the patent application titled “Method for MitigatingEffects of Interference in Impulse Radio Communication,” applicationSer. No. 09/587,033, filed Jun. 02, 1999, assigned to the assignee ofthe present invention, and if incorporated herein by reference.

Moderating Interference in Equipment Control Applications

Yet another improvement to impulse radio includes moderatinginterference with impulse radio wireless control of an appliance. Thecontrol is affected by a controller remote from the appliance whichtransmits impulse radio digital control signals to the appliance. Thecontrol signals have a transmission power and a data rate. The methodcomprises the steps of establishing a maximum acceptable noise value fora parameter relating to interfering signals and a frequency range formeasuring the interfering signals, measuring the parameter for theinterference signals within the frequency range, and effecting analteration of transmission of the control signals when the parameterexceeds the maximum acceptable noise value.

For greater elaboration of moderating interference while effectingimpulse radio wireless control of equipment, see patent applicationtitled “Method and Apparatus for Moderating Interference While EffectingImpulse Radio Wireless Control of Equipment,” application Ser. No.09/586,163, filed Jun. 2, 1999, and assigned to the assignee of thepresent invention, and incorporated herein by reference.

Exemplary Transceiver Implementation

Transmitter

An exemplary embodiment of an impulse radio transmitter 602 of animpulse radio communication system having an optional subcarrier channelwill now be described with reference to FIG. 6.

The transmitter 602 comprises a time base 604 that generates a periodictiming signal 606. The time base 604 typically comprises a voltagecontrolled oscillator (VCO), or the like, having a high timing accuracyand low jitter, on the order of picoseconds (ps). The control voltage toadjust the VCO center frequency is set at calibration to the desiredcenter frequency used to define the transmitter's nominal pulserepetition rate. The periodic timing signal 606 is supplied to aprecision timing generator 608.

The precision timing generator 608 supplies synchronizing signals 610 tothe code source 612 and utilizes the code source output 614, togetherwith an optional, internally generated subcarrier signal, and aninformation signal 616, to generate a modulated, coded timing signal618.

An information source 620 supplies the information signal 616 to theprecision timing generator 608. The information signal 616 can be anytype of intelligence, including digital bits representing voice, data,imagery, or the like, analog signals, or complex signals.

A pulse generator 622 uses the modulated, coded timing signal 618 as atrigger signal to generate output pulses. The output pulses are providedto a transmit antenna 624 via a transmission line 626 coupled thereto.The output pulses are converted into propagating electromagnetic pulsesby the transmit antenna 624. The electromagnetic pulses are called theemitted signal, and propagate to an impulse radio receiver 702, such asshown in FIG. 7, through a propagation medium. In a preferredembodiment, the emitted signal is wide-band or ultrawide-band,approaching a monocycle pulse as in FIG. 1B. However, the emitted signalmay be spectrally modified by filtering of the pulses, which may causethem to have more zero crossings (more cycles) in the time domain,requiring the radio receiver to use a similar waveform as the templatesignal for efficient conversion.

Receiver

An exemplary embodiment of an impulse radio receiver (hereinafter calledthe receiver) for the impulse radio communication system is nowdescribed with reference to FIG. 7.

The receiver 702 comprises a receive antenna 704 for receiving apropagated impulse radio signal 706. A received signal 708 is input to across correlator or sampler 710, via a receiver transmission line,coupled to the receive antenna 704. The cross correlation 710 produces abaseband output 712.

The receiver 702 also includes a precision timing generator 714, whichreceives a periodic timing signal 716 from a receiver time base 718.This time base 718 may be adjustable and controllable in time,frequency, or phase, as required by the lock loop in order to lock onthe received signal 708. The precision timing generator 714 providessynchronizing signals 720 to the code source 722 and receives a codecontrol signal 724 from the code source 722. The precision timinggenerator 714 utilizes the periodic timing signal 716 and code controlsignal 724 to produce a coded timing signal 726. The template generator728 is triggered by this coded timing signal 726 and produces a train oftemplate signal pulses 730 ideally having waveforms substantiallyequivalent to each pulse of the received signal 708. The code forreceiving a given signal is the same code utilized by the originatingtransmitter to generate the propagated signal. Thus, the timing of thetemplate pulse train matches the timing of the received signal pulsetrain, allowing the received signal 708 to be synchronously sampled inthe correlator 710. The correlator 710 preferably comprises a multiplierfollowed by a short term integrator to sum the multiplier product overthe pulse interval.

The output of the correlator 710 is coupled to a subcarrier demodulator732, which demodulates the subcarrier information signal from theoptional subcarrier. The purpose of the optional subcarrier process,when used, is to move the information signal away from DC (zerofrequency) to improve immunity to low frequency noise and offsets. Theoutput of the subcarrier demodulator is then filtered or integrated inthe pulse summation stage 734. A digital system embodiment is shown inFIG. 7. In this digital system, a sample and hold 736 samples the output735 of the pulse summation stage 734 synchronously with the completionof the summation of a digital bit or symbol. The output of sample andhold 736 is then compared with a nominal zero (or reference) signaloutput in a detector stage 738 to provide an output signal 739representing the digital state of the output voltage of sample and hold736.

The baseband signal 712 is also input to a lowpass filter 742 (alsoreferred to as lock loop filter 742). A control loop comprising thelowpass filter 742, time base 718, precision timing generator 714,template generator 728, and correlator 710 is used to generate an errorsignal 744. The error signal 744 provides adjustments to the adjustabletime base 718 to position in time the periodic timing signal 726 inrelation to the position of the received signal 708.

In a transceiver embodiment, substantial economy can be achieved bysharing part or all of several of the functions of the transmitter 602and receiver 702. Some of these include the time base 718, precisiontiming generator 714, code source 722, antenna 704, and the like.

FIGS. 8A-8C illustrate the cross correlation process and the correlationfunction. FIG. 8A shows the waveform of a template signal. FIG. 8B showsthe waveform of a received impulse radio signal at a set of severalpossible time offsets. FIG. 8C represents the output of the crosscorrelator for each of the time offsets of FIG. 8B. For any given pulsereceived, there is a corresponding point that is applicable on thisgraph. This is the point corresponding to the time offset of thetemplate signal used to receive that pulse. Further examples and detailsof precision timing can be found described in U.S. Pat. No. 5,677,927,and commonly owned co-pending application application Ser. No.09/146,524, filed Sep. 3, 1998, titled “Precision Timing GeneratorSystem and Method,” both of which are incorporated herein by reference.

Because of the unique nature of impulse radio receivers, severalmodifications have been recently made to enhance system capabilities.Modifications include the utilization of multiple correlators to measurethe impulse response of a channel to the maximum communications range ofthe system and to capture information on data symbol statistics.Further, multiple correlators enable rake pulse correlation techniques,more efficient acquisition and tracking implementations, variousmodulation schemes, and collection of time-calibrated pictures ofreceived waveforms. For greater elaboration of multiple correlatortechniques, see patent application titled “System and Method of usingMultiple Correlator Receivers in an Impulse Radio System”, applicationSer. No. 09/537,264, filed Mar. 29, 2000, assigned to the assignee ofthe present invention, and incorporated herein by reference.

Methods to improve the speed at which a receiver can acquire and lockonto an incoming impulse radio signal have been developed. In oneapproach, a receiver includes an adjustable time base to output asliding periodic timing signal having an adjustable repetition rate anda decode timing modulator to output a decode signal in response to theperiodic timing signal. The impulse radio signal is cross-correlatedwith the decode signal to output a baseband signal. The receiverintegrates T samples of the baseband signal and a threshold detectoruses the integration results to detect channel coincidence. A receivercontroller stops sliding the time base when channel coincidence isdetected. A counter and extra count logic, coupled to the controller,are configured to increment or decrement the address counter by one ormore extra counts after each T pulses is reached in order to shift thecode modulo for proper phase alignment of the periodic timing signal andthe received impulse radio signal. This method is described in moredetail in U.S. Pat. No. 5,832,035 to Fullerton, incorporated herein byreference.

In another approach, a receiver obtains a template pulse train and areceived impulse radio signal. The receiver compares the template pulsetrain and the received impulse radio signal. The system performs athreshold check on the comparison result. If the comparison resultpasses the threshold check, the system locks on the received impulseradio signal. The system may also perform a quick check, asynchronization check, and/or a command check of the impulse radiosignal. For greater elaboration of this approach, see the patentapplication titled “Method and System for Fast Acquisition of UltraWideband Signals,” application Ser. No. 09/538,292, filed Mar. 29, 2000,assigned to the assignee of the present invention, and incorporatedherein by reference.

A receiver has been developed that includes a baseband signal converterdevice and combines multiple converter circuits and an RF amplifier in asingle integrated circuit package. For greater elaboration of thisreceiver, see the patent application titled “Baseband Signal Converterfor a Wideband Impulse Radio Receiver,” application Ser. No. 09/356,384,filed Jul. 16, 1999, assigned to the assignee of the present invention,and incorporated herein by reference.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 9-24, there are disclosed a system 900, an electronicdevice 910 and a method 1200 in accordance with the present invention.Although the present invention is described as being used on a footballfield, it should be understood that the present invention can be used inmany different sporting venues including, for example, a baseball field,soccer field, hockey rink, basketball court or any sports environment inwhich people train and compete. Accordingly, the system 900, electronicdevice 910 and method 1200 should not be construed in a limited manner.

Referring to FIG. 9, there is a diagram illustrating the basiccomponents of the system 900 in accordance with the present invention.Essentially, the system 900 includes an electronic device 910 (only oneshown) and a central station 930. The electronic device 910 is attachedto any desired location on an athlete 920 which can be one of many suchathletes playing on a field 1100 (see FIG. 11). The electronic device910 is capable of transmitting and receiving impulse radio signals 915to and from the central station 930. In particular, the impulse radiosignals 915 convey information using a known pseudorandom sequence ofpulses that look like a series of Gaussian waveforms (see FIGS. 1-3).The information conveyed in the impulse radio signals enables people(e.g., coaches 940 a, broadcasters 940 b, fans 940 c) to track theposition of the athlete 920 as he/she moves around the field 1100 and/orenables secure communications to occur between the athlete 920 and theirteammates, fans or coaches. For clarity, only the broadcaster 940 b andone athlete 920 are shown in FIG. 9. To accomplish these tasks, both theelectronic device 910 and central station 930 can incorporate one chipthat enables the revolutionary and highly scalable communicationcapabilities and position capabilities of impulse radio technology.Essentially, the electronic device 910, other electronic devices 910 andthe central station 930 can use impulse radio signals 915 to transmitand receive information to and from one another in places and situationsnot possible with traditional tracking and communication systems.

Traditional tracking systems generally use the well known GlobalPositioning System (GPS) based technology to determine the position of aperson or object. Unfortunately, GPS based technology is not suitablefor tracking athletes 920 within an enclosed arena because of thedifficulty a GPS unit has in communicating with GPS satellites throughthe roof, outer walls and inner walls of the arena. Even if the arena isnot enclosed, GPS based technology is not able to meet the needs of thepresent invention due to the physical constraints and power requirementsof a GPS unit that must be carried by the athletes 920. For instance,the use of GPS based technology would require that each athlete 920carry a relatively large GPS unit that is made up of GPS electronics,memory, logic, a R/F transceiver and a battery. As such, the GPS unit isnot small enough to be conveniently carried by the athlete 920.

Another problem with the GPS unit is that it provides a roughapproximation of the position of the athlete 920 on a field 1100. Theapproximation of the position is usually rough due to selectiveauthority (now disabled) and atmospheric alterations. Selectiveauthority was a government-controlled way of making GPS based technologyinaccurate for defense purposes. GPS units can attempt to mitigateselective authority inaccuracies and other inaccuracies by utilizing acorrection signal received from a base station on or near the field 1100or from another satellite. However, GPS units that receive thiscorrection signal still generate an inaccurate measurement that may beoff five or more meters. To date there is nothing that can compensatefor atmospheric alterations which are an inherent problem with GPS basedtechnology. Moreover, GPS based technology suffers from a highlyunreliable infrastructure because the GPS unit requires that at leasttwo separate signals from two separate satellites be received at alltimes to remain operable. However, impulse radio technology enables veryprecise position calculations having an accuracy of less than +/−2centimeters to occur in less than a second, which is a markedimprovement over the traditional GPS based technology.

Traditional communication systems used to transmit and receive radiosignals between a traditional central station and traditional electronicdevices within a sports arena often suffer from the adverse affects of“dead zones” and “multipath interference”. Dead zones in a sports arenamake it difficult for a central station to enable communications with anelectronic device attached to an athlete using standard radio signals.For instance, the standard radio signals sent from the standard radiotransceiver attached to the central station may not be able to penetratea certain wall or floor within the building and as such may not reachthe standard radio transceiver attached to the athlete. This isespecially true when the athlete moves to different locations within thesports arena. Fortunately in the present invention, the impulse radiosignals 915 transmitted between the electronic device 910 and centralstation 930 are located very close to DC which makes the attenuation dueto walls, stands and roof minimal when compared to standard radiosignals.

In addition, “multipath interference” which is very problematic withinthe closed structure of a sports arena can be caused by the interferenceof a standard radio signal that has reached either the traditionalelectronic device or traditional central station by two or more paths.Essentially, a standard radio receiver attached to a athlete may not beable to demodulate a radio signal because the originally transmittedradio signal effectively cancels itself out by bouncing of the walls,roof (if any) and stands of the sports arena before reaching the athleteand vice versa. The present invention is not affected by “multipathinterference” because the impulses of the impulse radio signals 915delayed by multipath reflections typically arrive outside a correlation(or demodulation) period of the receiving impulse radio unit.

Moreover, traditional central stations use either standard radio orinfrared electromagnetic waves to transfer data to and from atraditional electronic device. However, these traditional communicationmeans impose undesirable limits on range, data rate and communicationquality. For instance, traditional wireless communication technologiessuffer from the following undesirable characteristics:

Have limited spectral bandwidth.

Have shared broadcast medium.

Are unprotected from outside signals.

In contrast, the use of impulse radio technology in the presentinvention provides many advantages over traditional wirelesscommunication technologies including, for example, the following:

Ultra-short duration pulses which yield ultrawide bandwidth signals.

Extremely low power spectral densities.

Excellent immunity to interference from other radio systems.

Consumes substantially less power than conventional radios.

Capable of high bandwidth and multi-channel performance.

Referring to FIG. 10, there is a diagram illustrating in greater detailthe electronic device 910 in accordance with the present invention. Asillustrated in FIG. 10, the electronic device 910 incorporates a firstimpulse radio unit 1002. And, as illustrated in FIG. 9, the centralstation 930 incorporates a second impulse radio unit 1004. Each impulseradio unit 1002 and 1004 can be configured as a transceiver and includea receiving impulse radio unit 602 and a transmitting impulse radio unit702 (see FIGS. 6 and 7). In the alternative, the impulse radio units1002 and 1004 can be configured as either a receiver or transmitterdepending on the functional requirements of the central station 930 andelectronic device 910. For instance, the central station may only needto download information and, as such, the first impulse radio unit 1002could be a transmitting impulse radio unit and the second impulse radiounit 1004 would be a receiving impulse radio unit. Again, the centralstation 930 and electronic device 910 use impulse radio signals 915 totransmit and receive information to and from one another in places andsituations not possible with standard radio signals.

The electronic device 910 may also include an interface unit 1008 (e.g.,speaker, microphone) that enables two-way impulse radio secured voicecommunications between the athlete 920 and other people includingcoaches 940 a, broadcasters 940 b, fans 940 c and other athletes 920(see FIG. 11). In addition to enabling secure communications, impulseradio technology can also enable the central station 930 to track theposition of the electronic device 910 attached to the athlete 920. Todetermine the current position of the electronic device 910, the firstimpulse radio unit 1002 associated with the electronic device 910interacts with one or more reference impulse radio units 1102 (see FIG.11) such that either the electronic device 910, the central station 930,or one of the reference impulse radio units 1102 can calculate thecurrent position of the electronic device 910. How the impulse radiounits 1002 and 1004 interact with one another to determine the positionof the electronic device 910 can best be understood by referring to thedescription associated with FIGS. 11 and 13-24.

The electronic device 910 may also incorporate or interact with one ormore sensors 1006. For instance, the sensor 1006 can be attached in anymanner to the athlete 920 and is capable of functioning as a heart ratemonitor, blood pressure monitor, blood monitor, temperature monitorand/or perspiration monitor. In particular, the sensor 1006 can monitorone or more vital signs of the athlete 920 and forward that informationto the first impulse radio unit 1002 which, in turn, modulates andforwards the information using high bandwidth impulse radio signals 915to the central station 930. The sensor 1006 can have a hardwireconnection or wireless connection (as shown) to the electronic device910.

A variety of monitoring techniques that can be used in the presentinvention have been disclosed in U.S. patent application Ser. No.09/407,106. For instance, the central station 930 can remotely activatethe sensor(s) 1006 to monitor any one of the vital signs of the athlete920. Each sensor 1006 can also be designed to compare a sensed vitalsign to a predetermined range of acceptable conditions. And, in theevent the sensor 1006 monitors a vital sign that falls outside of apredetermined range of acceptable conditions, then the electronic device910 can send an alert to the central station 930. For instance, thesensor 1006 can send an alert whenever one of the at least one monitoredvital signs indicates that an illegal substance has detected on theathlete 920.

Referring to FIG. 11, there is a diagram illustrating a system 900 thatcan be used on a football field 1100. As illustrated, the football field1100 includes the playing field 1104, side lines 1105 and a grandstand1106. The grandstand 1106 is where broadcasters 940 b can use thecentral station 930 and fans 940 c can use handheld units 1108 a whichoperate in a similar manner as the central station 930. And, the sidelines 1105 are where one or more coaches 940 a or other athletes 920 canuse handheld units 1108 b which operate in a similar manner as thecentral station 930. Of course, the athletes 920 (shown as Xs and Os) onthe playing field 1104 and the athletes 920 on the side lines 1105 canalso carry an electronic device 910. It should be understood that theillustrated layout of football field 1100 is for purposes of discussiononly and is not intended as a limitation to the present invention whichcan operate in a wide variety of sporting venues.

The reference impulse radio units 1102 (only 8 shown) have knownpositions and are located to provide maximum coverage on the footballfield 1100. The central station 930 typically has a wireless connectionor hardwire connection to the reference impulse radio units 1102, andthe electronic device 910 typically has a wireless connection to thereference impulse radio units 1102. Each athlete 920 can carry anelectronic device 910 that is capable of interacting with one or more ofthe reference impulse radio units 1102 such that either the electronicdevice 910, the central station 930, or one of the reference impulseradio units 1102 can calculate the current position and track themovement of the athlete 920. Moreover, a football 1107 (or any otherpiece of sports equipment such as a soccer ball, baseball, hockey puckor the like) can carry an electronic device 910 or an impulse radio unitthat is capable of interacting with one or more of the reference impulseradio units 1102 such that either the electronic device 910, the centralstation 930, or one of the reference impulse radio units 1102 cancalculate the current position and track the movement of the football1107. A variety of impulse radio positioning networks (e.g., two or morereference impulse radio units 1102 and one or more electronic devices910) that enable the present invention to perform the positioning andtracking functions are described in greater detail below with respect toFIGS. 13-24.

For instance, the positioning and tracking functions can be accomplishedby stepping through several steps. The first step is for the referenceimpulse radio units 1102 to synchronize together and begin passinginformation. Then, when an electronic device 910 enters or is powered-upon the football field 1100, it synchronizes itself to the previouslysynchronized reference impulse radio units 1102. Once the electronicdevice 910 is synchronized, it begins collecting and time-tagging rangemeasurements from any available reference impulse radio units 1102. Theelectronic device 910 then takes these time-tagged ranges and, using aleast squares-based or similar estimator, calculates its position on thefootball field 1100. Alternatively, one of the reference impulse radiounits 1102 can calculate the position of the electronic device 910 whichis attached to a known athlete 920.

Thereafter, the electronic device 910 or one of the reference impulseradio units 1102 forwards its position calculation to the centralstation 930 for storage and/or real-time display. The central station930 could then calculate the time it takes the athlete 920 or football1107 to travel from one position on the football field 1100 to anotherposition on the football field 1100. In addition, the central station930 can forward these position and time calculations to the handheldunits 1108 a and 1108 b for storage and/or real-time display.

It should be understood that the central station 930 and each handheldunit 1108 a and 1108 b can be programmed to track only the athletes(s)920 that the broadcasters 940 b and other people 920, 940 a and 940 cwant to watch at one time. Moreover, the central station 930, electronicdevice 910 and handheld units 1108 a and 1108 b can each be programmedto sound an alarm whenever one of the monitored vital signs (e.g., bloodpressure, heart rate) of one of the athletes 920 falls outside apredetermined range of acceptable conditions. As such, the coaches 940 acan use the monitored vital signs of the athlete 920 to help assist themin the physical conditioning and training of that athlete 920.

The central station 930 may also provide a variety of sports relatedinformation to the users of the handheld units 1108 a and 1108 b. Thesports related information can include the same type of information thatis often found in the program guides and various statistic books. Forinstance, the sports related information may also include real-timescores of other games and/or details about the history of a particularathlete 920 including that athlete's past statistics, previous teams etc. . . Each user may have to pay a predetermined fee to rent a handheldunit 1108 a or 1108 b where the fee is based on the type and amount ofsports related information that can be assessed by the handheld unit andthe other capabilities of the handheld unit.

The central station 930 may also provide an Internet site 1110 and otherfootball fields, gambling halls, television stations with the currentpositions of the athletes 920 on the football field 1100, the monitoredvital signs of each athlete 920 and/or other sports related information.Thus, fans (not shown) can watch the game on their computer (ortelevision) and at the same time obtain all the details they would wantto know about a specific athlete 920. The game (or play) shown on thecomputer or television may just show moving numbers or similar indiciaof the moving athletes 920 and not the athletes 920 themselves.

In particular, the central station 930 can use Kalman filtering, splinecurve fitting and other techniques to perform multilateration on thereceived positioning data to determine the position and/or velocity ofone or more athletes 920. The position and/or velocity data can be usedto represent the path of each athlete 920 during a play, which can beviewed instantaneously. In other words, accurate positions of allathletes 920 could be reflected on a screen (e.g., computer,television). And, the varying velocities of the athletes 920 could alsobe reflected on the screen.

Referring to FIG. 12, there is a flowchart illustrating the basic stepsof a preferred method 1200 for tracking an athlete and/or for enablingcommunications between the athlete and their teammates, fans or coachesin accordance with the present invention. Beginning at step 1202, theelectronic device 910 (including the impulse radio unit 1002) isattached to an athlete 920.

At step 1204, the electronic device 910 includes a sensor 1006 that iscoupled to the athlete 920 which enables the monitoring of at least onevital sign of the athlete 920. As described above, the sensor 1006 iscapable of functioning as a heart rate monitor, blood pressure monitor,blood monitor and/or perspiration monitor (for example). The centralstation 930 and handheld units 1108 a and 1108 b can display and/ormonitor the one or more vital signs of the athlete 920, and can sound analert upon detecting any health related problems or detecting thepresence of any illegal substance(s) on the athlete 920.

As mentioned earlier, the sensor 1006 can be remotely activated by thecentral station 930 to monitor any one of the vital signs of the athlete920. The sensor 1006 can also be programmed to compare a monitored vitalsign to a predetermined range of acceptable conditions. And, in theevent the sensor 1006 monitors a vital sign that falls outside of apredetermined range of acceptable conditions, then the electronic device910 can send an alert to the central station 930.

At step 1206, the electronic device 910 can determine the currentlocation of an athlete 920 on the football field 1100 by interactingwith a predetermined number of reference impulse radio units 1102. Aftercompleting or during the progress of each step 1204 and 1206, theelectronic device 910 operates to forward to the central station 930 aseries of impulse radio signals 915 containing information including,for example, the monitored vital signs of the athlete 920 and/or thecurrent position of the athlete 920 on the football field 1100. Itshould be noted that one or more of the reference impulse radio units1102 and the central station 930 are also capable of determining thecurrent position of the athlete 920 on the football field 1100.

At step 1208, the central station 930 is operable to display all or aselected portion of the information received from the electronic device910. Again, the information that can be displayed includes the monitoredvital sign(s) of the athlete 920 and/or the current position of theathlete 920 (and other athletes 920) on the football field 1100. Thecentral station 930 can also display an alarm whenever one of themonitored vital signs of the athlete 920 exceeds a predeterminedthreshold. Moreover, the central station 930 is capable of distributingthis information to the handheld units 1108 a and 1108 b and/or theInternet site 1110. Like, the central station 930 each of the handheldunits 1108 a and 1108 b, the Internet site 1110 can all display anoverlay of the football field 1100 that indicates the position of eachmoving athlete 920 and/or the monitored vital signs of each athlete 920along with other sports related information.

At step 1210, the electronic device 912 can enable two-way securecommunications between the athlete 920 and other people such as coaches940 a, broadcasters 940 b, fans 940 c and other athletes. For instance,one athlete 920 (e.g., quarterback) can communicate in a secure mannerwith the coaches 940 a. Or, the coaches 940 a on one team can talk toone another in a secure manner using impulse radio technology.

At step 1212, the central station 930 may also provide a variety ofsports related information to the users of the handheld units 1108 a and1108 b, the Internet site 1110. The sports related information caninclude the same type of information that is often found in the programguides and various statistic books. For instance, the sports relatedinformation may include real time scores of other games and/or detailsabout the history of a particular athlete 920 including that athlete'spast statistics, previous teams etc . . . Each user may have to pay apredetermined fee to rent a handheld unit 1108 a or 1108 b where the feeis based on the type and amount of sports related information that canbe assessed by the handheld unit and the other capabilities of thehandheld unit.

Impulse Radio Positioning Networks

A variety of impulse radio positioning networks capable of performingthe positioning and tracking functions of the present invention aredescribed in this Section (see also U.S. patent application Ser. No.09/456,409). An impulse radio positioning network includes a set ofreference impulse radio units 1102 (shown below as reference impulseradio units R1-R6), one or more electronic devices 910 (shown below aselectronic devices M1-M3) and a central station 930.

Synchronized Transceiver Tracking Architecture

Referring to FIG. 13, there is illustrated a block diagram of an impulseradio positioning network 1300 utilizing a synchronized transceivertracking architecture. This architecture is perhaps the most generic ofthe impulse radio positioning networks since both electronic devices M1and M2 and it reference impulse radio units R1-R4 are full two-waytransceivers. The network 1300 is designed to be scalable, allowing fromvery few electronic devices M1 and M2 and reference impulse radio unitsR1-R4 to a very large number.

This particular example of the synchronized transceiver trackingarchitecture shows a network 1300 of four reference impulse radio unitsR1-R4 and two electronic devices M1 and M2. The arrows between theradios represent two-way data and/or voice links. A fullyinter-connected network would have every radio continually communicatingwith every other radio, but this is not required and can be dependentupon the needs of the particular application.

Each radio is a two-way transceiver; thus each link between radios istwo-way (duplex). Precise ranging information (the distance between tworadios) is distributed around the network 1300 in such a way as to allowthe electronic devices M1 and M2 to determine their precisethree-dimensional position within a local coordinate system. Thisposition, along with other data or voice traffic, can then be relayedfrom the electronic devices M1 and M2 back to the reference masterimpulse radio unit R1, one of the other reference relay impulse radiounits R2-R4 or the central station 930.

The radios used in this architecture are impulse radio two-waytransceivers. The hardware of the reference impulse radio units R1-R4and electronic devices M1 and M2 is essentially the same. The firmware,however, varies slightly based on the functions each radio must perform.For example, the reference master impulse radio unit RP directs thepassing of information and is typically responsible for collecting allthe data for external graphical display at the central station 930. Theremaining reference relay impulse radio units R2-R4 contain a separateversion of the firmware, the primary difference being the differentparameters or information that each reference relay impulse radio unitR2-R4 must provide the network. Finally, the electronic devices M1 andM2 have their own firmware version that calculates their position.

In FIG. 13, each radio link is a two-way link that allows for thepassing of information, both data and/or voice. The data-rates betweeneach radio link is a function of several variables including the numberof pulses integrated to get a single bit, the number of bits per dataparameter, the length of any headers required in the messages, the rangebin size, and the number of radios in the network.

By transmitting in assigned time slots and by carefully listening to theother radios transmit in their assigned transmit time slots, the entiregroup of radios within the network, both electronic devices M1 and M2and reference impulse radio units R1-R4, are able to synchronizethemselves. The oscillators used on the impulse radio boards driftslowly in time, thus they may require continual monitoring andadjustment of synchronization. The accuracy of this synchronizationprocess (timing) is dependent upon several factors including, forexample, how often and how long each radio transmits.

The purpose of this impulse radio positioning network 1300 is to enablethe tracking of the electronic devices M1 and M2. Tracking isaccomplished by stepping through several well-defined defined steps. Thefirst step is for the reference impulse radio units R1-R4 to synchronizetogether and begin passing information. Then, when an electronic deviceM1 or M2 enters the network area, it synchronizes itself to thepreviously synchronized reference impulse radio units R1-R4. Once theelectronic device M1 or M2 is synchronized, it begins collecting andtime-tagging range measurements from any available reference impulseradio units R1-R4 (or other electronic device M1 or M2). The electronicdevice M1 or M2 then takes these time-tagged ranges and, using a leastsquares-based or similar estimator, calculates the position of theelectronic device M1 or M2 in local coordinates. If the situationwarrants and the conversion possible, the local coordinates can beconverted to any one of the worldwide coordinates such as Earth CenteredInertial (ECI), Earth Centered Earth Fixed (ECEF), or J2000 (inertialcoordinates fixed to year 2000). Finally, the electronic device M1 or M2forwards its position calculation to the central station 930 for storageand real-time display.

Unsynchronized Transceiver Tracking Architecture

Referring to FIG. 14, there is illustrated a block diagram of an impulseradio positioning network 1400 utilizing an unsynchronized transceivertracking architecture. This architecture is similar to synchronizedtransceiver tracking of FIG. 14, except that the reference impulse,radio units R1-R4 are not time-synchronized. Both the electronic devicesM1 and M2 and reference impulse radio units R1-R4 for this architectureare full two-way transceivers. The network is designed to be scalable,allowing from very few electronic devices M1 and M2 and referenceimpulse radio units R1-R4 and to a very large number.

This particular example of the unsynchronized transceiver trackingarchitecture shows a network 1400 of four reference impulse radio unitsR1-R4 and two electronic devices M1 and M2. The arrows between theradios represent two-way data and/or voice links. A fullyinter-connected network would have every radio continually communicatingwith every other radio, but this is not required and can be defined asto the needs of the particular application.

Each radio is a two-way transceiver; thus each link between radios istwo-way (duplex). Precise ranging information (the distance between tworadios) is distributed around the network in such a way as to allow theelectronic devices M1 and M2 to determine their precisethree-dimensional position within a local coordinate system. Thisposition, along with other data or voice traffic, can then be relayedfrom the electronic devices M1 and M2 back to the reference masterimpulse radio unit R1, one of the other reference relay impulse radiounits R2-R3 or the central station 930.

The radios used in the architecture of FIG. 14 are impulse radio two-waytransceivers. The hardware of the reference impulse radio units R1-R4and electronic devices M1 and M2 is essentially the same. The firmware,however, varies slightly based on the functions each radio must perform.For example, the reference master impulse radio unit R1 directs thepassing of information, and typically is responsible for collecting allthe data for external graphical display at the central station 930. Theremaining reference relay impulse radio units R2-R4 contain a separateversion of the firmware, the primary difference being the differentparameters or information that each reference relay radio must providethe network. Finally, the electronic devices M1 and M2 have their ownfirmware version that calculates their position and displays it locallyif desired.

In FIG. 14, each radio link is a two-way link that allows for thepassing of information, data and/or voice. The data-rates between eachradio link is a function of several variables including the number ofpulses integrated to get a single bit, the number of bits per dataparameter, the length of any headers required in the messages, the rangebin size, and the number of radios in the network.

Unlike the radios in the synchronized transceiver tracking architecture,the reference impulse radio units R1-R4 in this architecture are nottime-synchronized as a network. These reference impulse radio unitsR1-R4 operate independently (free-running) and provide ranges to theelectronic devices M1 and M2 either periodically, randomly, or whentasked. Depending upon the application and situation, the referenceimpulse radio units R1-R4 may or may not talk to other reference radiosin the network.

As with the architecture of FIG. 13, the purpose of this impulse radiopositioning network 1400 is to enable the tracking of electronic devicesM1 and M2. Tracking is accomplished by stepping through several steps.These steps are dependent upon the way in which the reference impulseradio units R1-R4 range with the electronic devices M1 and M2(periodically, randomly, or when tasked). When a electronic device M1 orM2 enters the network area, it either listens for reference impulseradio units R1-R4 to broadcast, then responds, or it queries (tasks) thedesired reference impulse radio units R1-R4 to respond. The electronicdevice M1 or M2 begins collecting and time-tagging range measurementsfrom reference (or other mobile) radios. The electronic device M1 or M2then takes these time-tagged ranges and, using a least squares-based orsimilar estimator, calculates the position of the electronic device M1or M2 in local coordinates. If the situation warrants and the conversionpossible, the local coordinates can be converted to any one of theworldwide coordinates such as Earth Centered Inertial (ECI), EarthCentered Earth Fixed (ECEF), or J2000 (inertial coordinates fixed toyear 2000). Finally, the electronic device M1 or M2 forwards itsposition calculation to the central station 930 for storage andreal-time display.

Synchronized Transmitter Tracking Architecture

Referring to FIG. 15, there is illustrated a block diagram of an impulseradio positioning network 1500 utilizing a synchronized transmittertracking architecture. This architecture is perhaps the simplest of theimpulse radio positioning architectures, from the point-of-view of theelectronic devices M1 and M2, since the electronic devices M1 and M2simply transmit in a free-running sense. The network is designed to bescalable, allowing from very few electronic devices M1 and M2 andreference impulse radio units R1-R4 to a very large number. Thisarchitecture is especially applicable to an “RF tag” (radio frequencytag) type of application.

This particular example of synchronized transmitter trackingarchitecture shows a network 1500 of four reference impulse radio unitsradios R1-R4 and two electronic devices M1 and M2. The arrows betweenthe radios represent two-way and one-way data and/or voice links. Noticethat the electronic devices M1 and M2 only transmit, thus they do notreceive the transmissions from the other radios.

Each reference impulse radio unit R1-R4 is a two-way transceiver; thuseach link between reference impulse radio units R1-R4 is two-way(duplex). Precise ranging information (the distance between two radios)is distributed around the network in such a way as to allow thesynchronized reference impulse radio units R1-R4 to receivetransmissions from the electronic devices M1 and M2 and then determinethe three-dimensional position of the electronic devices M1 and M2. Thisposition, along with other data or voice traffic, can then be relayedfrom reference relay impulse radio units R2-R4 back to the referencemaster impulse radio unit R1 or the central station 930.

The reference impulse radio units R1-R4 used in this architecture areimpulse radio two-way transceivers, the electronic devices M1 and M2 areone-way transmitters. The firmware in the radios varies slightly basedon the functions each radio must perform. For example, the referencemaster impulse radio unit R1 is designated to direct the passing ofinformation, and typically is responsible for collecting all the datafor external graphical display at the central station 930. The remainingreference relay impulse radio units R2-R4 contain a separate version ofthe firmware, the primary difference being the different parameters orinformation that each reference relay impulse radio unit R2-R4 mustprovide the network. Finally, the electronic devices M1 and M2 havetheir own firmware version that transmits pulses in predeterminedsequences.

Each reference radio link is a two-way link that allows for the passingof information, data and/or voice. The data-rates between each radiolink is a function of several variables including the number of pulsesintegrated to get a single bit, the number of bits per data parameter,the length of any headers required in the messages, the range bin size,and the number of radios in the network.

By transmitting in assigned time slots and by carefully listening to theother radios transmit in their assigned transmit time slots, the entiregroup of reference impulse radio units R1-R4 within the network are ableto synchronize themselves. The oscillators used on the impulse radioboards drift slowly in time, thus they may require monitoring andadjustment to maintain synchronization. The accuracy of thissynchronization process (timing) is dependent upon several factorsincluding, for example, how often and how long each radio transmitsalong with other factors. The electronic devices M1 and M2, since theyare transmit-only transmitters, are not time-synchronized to thesynchronized reference impulse radio units R1-R4.

The purpose of the impulse radio positioning network is to enable thetracking of electronic devices M1 and M2. Tracking is accomplished bystepping through several well-defined steps. The first step is for thereference impulse radio units R1-R4 to synchronize together and beginpassing information. Then, when a electronic device M1 or M2 enters thenetwork area and begins to transmit pulses, the reference impulse radiounits R1-R4 pick up these pulses as time-of-arrivals (TOAs). MultipleTOAs collected by different synchronized reference impulse radio unitsR1-R4 are then converted to ranges, which are then used to calculate theXYZ position of the electronic device M1 or M2 in local coordinates. Ifthe situation warrants and the conversion possible, the localcoordinates can be converted to any one of the worldwide coordinatessuch as Earth Centered Inertial (ECI), Earth Centered Earth Fixed(ECEF), or J2000 (inertial coordinates fixed to year 2000). Finally, thereference impulse radio units R1-R4 forward their position calculationto the central station 930 for storage and real-time display.

Unsynchronized Transmitter Tracking Architecture

Referring to FIG. 16, there is illustrated a block diagram of an impulseradio positioning network 1600 utilizing an unsynchronized transmittertracking architecture. This architecture is very similar to thesynchronized transmitter tracking architecture except that the referenceimpulse radio units R1-R4 are not synchronized in time. In other words,both the reference impulse radio units R1-R4 and the electronic devicesM1 and M2 are free-running. The network is designed to be scalable,allowing from very few electronic devices M1 and M2 and referenceimpulse radio units R1-R4 to a very large number. This architecture isespecially applicable to an “RF tag” (radio frequency tag) type ofapplication.

This particular example of the unsynchronized transmitter trackingarchitecture shows a network 1900 of four reference impulse radio unitsR1-R4 and two electronic devices M1 and M2. The arrows between theradios represent two-way and one-way data and/or voice links. Noticethat the electronic devices M1 and M2 only transmit, thus they do notreceive the transmissions from the other radios. Unlike the synchronoustransmitter tracking architecture, the reference impulse radio unitsR1-R4 in this architecture are free-running (unsynchronized). There areseveral ways to implement this design, the most common involves relayingthe time-of-arrival (TOA) pulses from the electronic devices M1 and M2and reference impulse radio units R1-R4, as received at the referenceimpulse radio units R1-R4, back to the reference master impulse radiounit R1 which communicates with the central station 930.

Each reference impulse radio unit R1-R4 in this architecture is atwo-way impulse radio transceiver; thus each link between referenceimpulse radio unit R1-R4 can be either two-way (duplex) or one-way(simplex). TOA information is typically transmitted from the referenceimpulse radio units R1-R4 back to the reference master impulse radiounit R1 where the TOAs are converted to ranges and then an XYZ positionof the electronic device M1 or M2, which can then be forwarded anddisplayed at the central station 930.

The reference impulse radio units R1-R4 used in this architecture areimpulse radio two-way transceivers, the electronic devices M1 and M2 areone-way impulse radio transmitters. The firmware in the radios variesslightly based on the functions each radio must perform. For example,the reference master impulse radio R1 collects the TOA information, andis typically responsible for forwarding this tracking data to thecentral station 930. The remaining reference relay impulse radio unitsR2-R4 contain a separate version of the firmware, the primary differencebeing the different parameters or information that each reference relayimpulse radio units R2-R4 must provide the network. Finally, theelectronic devices M1 and M2 have their own firmware version thattransmits pulses in predetermined sequences.

Each reference radio link is a two-way link that allows for the passingof information, data and/or voice. The data-rates between each radiolink is a function of several variables including the number of pulsesintegrated to get a single bit, the number of bits per data parameter,the length of any headers required in the messages, the range bin size,and the number of radios in the network.

Since the reference impulse radio units R1-R4 and electronic devices M1and M2 are free-running, synchronization is actually done by thereference master impulse radio unit R1. The oscillators used in theimpulse radios drift slowly in time, thus they may require monitoringand adjustment to maintain synchronization at the reference masterimpulse radio unit R1. The accuracy of this synchronization (timing) isdependent upon several factors including, for example, how often and howlong each radio transmits along with other factors.

The purpose of the impulse radio positioning network is to enable thetracking of electronic devices M1 and M2. Tracking is accomplished bystepping through several steps. The most likely method is to have eachreference impulse radio unit R1-R4 periodically (randomly) transmit apulse sequence. Then, when a electronic device M1 or M2 enters thenetwork area and begins to transmit pulses, the reference impulse radiounits R1-R4 pick up these pulses as time-of-arrivals (TOAs) as well asthe pulses (TOAs) transmitted by the other reference radios. TOAs canthen either be relayed back to the reference master impulse radio unitR1 or just collected directly (assuming it can pick up all thetransmissions). The reference master impulse radio unit R1 then convertsthese TOAs to ranges, which are then used to calculate the XYZ positionof the electronic device M1 or M2. If the situation warrants and theconversion possible, the XYZ position can be converted to any one of theworldwide coordinates such as Earth Centered Inertial (ECI), EarthCentered Earth Fixed (ECEF), or J2000 (inertial coordinates fixed toyear 2000). Finally, the reference master impulse radio unit R1 forwardsits position calculation to the central station 930 for storage andreal-time display.

Synchronized Receiver Tracking Architecture

Referring to FIG. 17, there is illustrated a block diagram of an impulseradio positioning network 1700 utilizing a synchronized receivertracking architecture. This architecture is different from thesynchronized transmitter tracking architecture in that in this designthe electronic devices M1 and M2 determine their positions but are notable to broadcast it to anyone since they are receive-only radios. Thenetwork is designed to be scalable, allowing from very few electronicdevices M1 and M2 and reference impulse radio units R1-R4 to a verylarge number.

This particular example of the synchronized receiver trackingarchitecture shows a network 2000 of four reference impulse radio unitsR1-R4 and two electronic devices M1 and M2. The arrows between theradios represent two-way and one-way data and/or voice links. Noticethat the electronic devices M1 and M2 receive transmissions from otherradios, and do not transmit.

Each reference impulse radio unit R1-R4 is a two-way transceiver, andeach electronic device M1 and M2 is a receive-only radio. Precise,synchronized pulses are transmitted by the reference network andreceived by the reference impulse radio units R1-R4 and the electronicdevices M1 and M2. The electronic devices M1 and M2 take thesetimes-of-arrival (TOA) pulses, convert them to ranges, then determinetheir XYZ positions. Since the electronic devices M1 and M2 do nottransmit, only they themselves know their XYZ positions.

The reference impulse radio units R1-R4 used in this architecture areimpulse radio two-way transceivers, the electronic devices M1 and M2 arereceive-only radios. The firmware for the radios varies slightly basedon the functions each radio must perform. For example, the referencemaster impulse radio unit R1 is designated to direct the synchronizationof the reference radio network. The remaining reference relay impulseradio units R2-R4 contain a separate version of the firmware, theprimary difference being the different parameters or information thateach reference relay impulse radio unit R2-R4 must provide the network.Finally, the electronic devices M1 and M2 have their own firmwareversion that calculates their position and displays it locally ifdesired.

Each reference radio link is a two-way link that allows for the passingof information, data and/or voice. The electronic devices M1 and M2 arereceive-only. The data-rates between each radio link is a function ofseveral variables including the number of pulses integrated to get asingle bit, the number of bits per data parameter, the length of anyheaders required in the messages, the range bin size, and the number ofradios in the network.

By transmitting in assigned time slots and by carefully listening to theother reference impulse radio units R1-R4 transmit in their assignedtransmit time slots, the entire group of reference impulse radio unitsR1-R4 within the network are able to synchronize themselves. Theoscillators used on the impulse radio boards may drift slowly in time,thus they may require monitoring and adjustment to maintainsynchronization. The accuracy of this synchronization (timing) isdependent upon several factors including, for example, how often and howlong each radio transmits along with other factors.

The purpose of the impulse radio positioning network is to enable thetracking of electronic devices M1 and M2. Tracking is accomplished bystepping through several well-defined steps. The first step is for thereference impulse radio units R1-R4 to synchronize together and beginpassing information. Then, when an electronic device M1 or M2 enters thenetwork area, it begins receiving the time-of-arrival (TOA) pulses fromthe reference radio network. These TOA pulses are converted to ranges,then the ranges are used to determine the XYZ position of the electronicdevice M1 or M2 in local coordinates using a least squares-basedestimator. If the situation warrants and the conversion possible, thelocal coordinates can be converted to any one of the worldwidecoordinates such as Earth Centered Inertial (ECI), Earth Centered EarthFixed (ECEF), or J2000 (inertial coordinates fixed to year 2000).

Unsynchronized Receiver Tracking Architecture

Referring to FIG. 18, there is illustrated a block diagram of an impulseradio positioning network 1800 utilizing an unsynchronized receivertracking architecture. This architecture is different from thesynchronized receiver tracking architecture in that in this design thereference impulse radio units R1-R4 are not time-synchronized. Similarto the synchronized receiver tracking architecture, electronic devicesM1 and M2 determine their positions but cannot broadcast them to anyonesince they are receive-only radios. The network is designed to bescalable, allowing from very few electronic devices M1 and M2 andreference impulse radio units R1-R4 to a very large number.

This particular example of the unsynchronized receiver trackingarchitecture shows a network 1800 of four reference impulse radio unitsR1-R4 and two electronic devices M1 and M2. The arrows between theradios represent two-way and one-way data and/or voice links. Noticethat the electronic devices M1 and M2 only receive transmissions fromother radios, and do not transmit.

Each reference impulse radio unit R1-R4 is an impulse radio two-waytransceiver, each electronic device M1 and M2 is a receive-only impulseradio. Precise, unsynchronized pulses are transmitted by the referencenetwork and received by the other reference impulse radio units R1-R4and the electronic devices M1 and M2. The electronic devices M1 and M2take these times-of-arrival (TOA) pulses, convert them to ranges, andthen determine their XYZ positions. Since the electronic devices M1 andM2 do not transmit, only they themselves know their XYZ positions.

The reference impulse radio units R1-R4 used in this architecture areimpulse radio two-way transceivers, the electronic devices M1 and M2 arereceive-only radios. The firmware for the radios varies slightly basedon the functions each radio must perform. For this design, the referencemaster impulse radio unit R1 may be used to provide some synchronizationinformation to the electronic devices M1 and M2. The electronic devicesM1 and M2 know the XYZ position for each reference impulse radio unitR1-R4 and as such they may do all of the synchronization internally.

The data-rates between each radio link is a function of severalvariables including the number of pulses integrated to get a single bit,the number of bits per data parameter, the length of any headersrequired in the messages, the range bin size, and the number of impulseradios in the network.

For this architecture, the reference impulse radio units R1-R4 transmitin a free-running (unsynchronized) manner. The oscillators used on theimpulse radio boards often drift slowly in time, thus requiringmonitoring and adjustment of synchronization by the reference masterimpulse radio unit R1 or the electronic devices M1 and M2 (whomever isdoing the synchronization). The accuracy of this synchronization(timing) is dependent upon several factors including, for example, howoften and how long each radio transmits.

The purpose of the impulse radio positioning network is to enable thetracking electronic devices M1 and M2. Tracking is accomplished bystepping through several steps. The first step is for the referenceimpulse radio units R1-R4 to begin transmitting pulses in a free-running(random) manner. Then, when an electronic device M1 or M2 enters thenetwork area, it begins receiving the time-of-arrival (TOA) pulses fromthe reference radio network. These TOA pulses are converted to ranges,then the ranges are used to determine the XYZ position of the electronicdevice M1 or M2 in local coordinates using a least squares-basedestimator. If the situation warrants and the conversion possible, thelocal coordinates can be converted to any one of the worldwidecoordinates such as Earth Centered Inertial (ECI), Earth Centered EarthFixed (ECEF), or J2000 (inertial coordinates fixed to year 2000).

Mixed Mode Tracking Architecture

For ease of reference, in FIGS. 19-24 the below legend applies.

Symbols and Definitions   Receiver Radio (receive only) X TransmitterRadio (transmit only)   Transceiver Radio (receive and transmit) R_(i)Reference Radio (fixed location) M_(i) Mobile Radio (radio beingtracked)   Duplex Radio Link   Simplex Radio Link

T O A, D T O A Time of Arrival, Differenced T O A

Referring to FIG. 19, there is illustrated a diagram of an impulse radiopositioning network 1900 utilizing a mixed mode reference radio trackingarchitecture. This architecture defines a network of reference impulseradio units R1-R6 comprised of any combination of transceivers (R₁, R₂,R₄, R₅), transmitters (R₃), and receivers (R₆). Electronic devices (noneshown) entering this mixed-mode reference network use whatever referenceradios are appropriate to determine their positions.

Referring to FIG. 20, there is a diagram of an impulse radio positioningnetwork 2000 utilizing a mixed mode mobile electronic device trackingarchitecture. Herein, the electronic devices M1-M3 are mixed mode andreference impulse radio units R1-R4 are likely time-synched. In thisillustrative example, the electronic device M1 is a transceiver,electronic device M2 is a transmitter, and electronic device M3 is areceiver. The reference impulse radio units R1-R4 can interact withdifferent types of electronic devices M1-M3 to help in the determinationof the positions of the mobile electronic devices.

Antennae Architectures

Referring to FIG. 21, there is illustrated a diagram of a steerable nullantennae architecture capable of being used in an impulse radiopositioning network. The aforementioned impulse radio positioningnetworks can implement and use steerable null antennae to help improvethe impulse radio distance calculations. For instance, all of thereference impulse radio units R1-R4 or some of them can utilizesteerable null antenna designs to direct the impulse propagation; withone important advantage being the possibility of using fewer referenceimpulse radio units or improving range and power requirements. Theelectronic device M1 can also incorporate and use a steerable nullantenna.

Referring to FIG. 22, there is illustrated a diagram of a specializeddifference antennae architecture capable of being used in an impulseradio positioning network. The reference impulse radio units R1-R4 ofthis architecture may use a difference antenna analogous to the phasedifference antenna used in GPS carrier phase surveying. The referenceimpulse radio units R1-R4 should be time synched and the electronicdevice M1 should be able to transmit and receive.

Referring to FIG. 23, there is illustrated a diagram of a specializeddirectional antennae architecture capable of being used in an impulseradio positioning network. As with the steerable null antennae design,the implementation of this architecture is often driven by designrequirements. The reference impulse radio units R1-R4 and the mobileelectronic device A1 can incorporate a directional antennae. Inaddition, the reference impulse radio units R1-R4 are likelytime-synched.

Referring to FIG. 24, there is illustrated a diagram of an amplitudesensing architecture capable of being used in an impulse radiopositioning network. Herein, the reference impulse radio units R1-R4 arelikely time-synched. Instead of the electronic device M1 and referenceimpulse radio units R1-R2 measuring range using TOA methods (round-trippulse intervals), signal amplitude is used to determine range. Severalimplementations can be used such as measuring the “absolute” amplitudeand using a pre-defined look up table that relates range to “amplitude”amplitude, or “relative” amplitude where pulse amplitudes from separateradios are differenced. Again, it should be noted that in this, as allarchitectures, the number of radios is for illustrative purposes onlyand more than one mobile impulse radio can be implemented in the presentarchitecture.

Although various embodiments of the present invention have beenillustrated in the accompanying Drawings and described in the foregoingDetailed Description, it should be understood that the invention is notlimited to the embodiments disclosed, but is capable of numerousrearrangements, modifications and substitutions without departing fromthe spirit of the invention as set forth and defined by the followingclaims.

What is claimed is:
 1. A method for tracking at least one athlete movingon a field, said method comprising the steps of: attaching, to eachathlete, an impulse radio unit; receiving, at a central station,information relating to a position of each athlete on the field;displaying, at the central station, an overlay of the field thatindicates the position of each athlete on the field; and displaying, ona television, an overlay of the field that indicates the position andrelative velocity of each athlete on the field.
 2. The method of claim1, further comprising the step of establishing secure communicationsbetween one or more of the athletes and people using the central stationor a handheld unit.
 3. The method of claim 1, further comprising thestep of determining the position of each athlete from the interactionbetween each impulse radio unit and at least two of a plurality ofreference impulse radio units.
 4. The method of claim 1, furthercomprising the step of displaying, on an Internet site, an overlay ofthe field that indicates the position and relative velocity of eachathlete on the field.
 5. The method of claim 1, further comprising thestep of displaying, at handheld units, an overlay of the field thatindicates the position and relative velocity of each athlete on thefield.
 6. The method of claim 1, further comprising the step ofproviding a variety of sports related information to a user of ahandheld unit and the central station.
 7. The method of claim 1, furthercomprising the step of coupling a sensor to at least one impulse radiounit, wherein the sensor is capable of monitoring at least one vitalsign of at least one athlete.
 8. A system for tracking at least oneathlete moving on a field, said system comprising: an impulse radio unitattached to each athlete; a central station capable of receivinginformation related to a position of each athlete on the field; saidcentral station is further capable of displaying an overlay of the fieldthat indicates the position of each athlete on the field; and saidcentral station is also capable of enabling a television to display anoverlay of the field that indicates the position and relative velocityof each athlete on the field.
 9. The system of claim 8, wherein peopleusing the central station or a handheld unit can communicate with one ormore of the athletes.
 10. The system of claim 8, further comprising thestep of determining the position of each athlete from the interactionbetween each impulse radio unit and at least two of a plurality ofreference impulse radio units.
 11. The system of claim 8, wherein saidcentral station is capable of enabling an Internet site to display anoverlay of the field that indicates the position and relative velocityof each athlete on the field.
 12. The system of claim 8, wherein saidcentral station is capable of enabling a handheld unit to display anoverlay of the field that indicates the position and relative velocityof each athlete on the field.
 13. The system of claim 8, wherein saidcentral station is capable of providing a variety of sports relatedinformation to a user of a handheld unit.
 14. The system of claim 8,wherein said central station is capable of tracking the movement of aball on the field.
 15. An electronic device comprising: an impulse radiounit, attached to an athlete, capable of interacting with at least tworeference impulse radio units in a manner which enables a centralstation to track a position of the athlete moving on a field and alsoenables the central station to enable handheld units to display anoverlay of the field that indicates the position and relative velocityof the athlete on the field.
 16. The electronic device of claim 15,further comprising an interface unit, coupled to the impulse radio unit,capable of enabling people using the central station or a handheld unitto communicate with the athlete.
 17. The electronic device of claim 15,further comprising a sensor, coupled to the impulse radio unit, capableof monitoring at least one vital sign of the athlete.
 18. A method fortracking an athlete and communicating with the athlete, said methodcomprising the steps of: attaching, to the athlete, an impulse radiounit; receiving, at a central station, information from the impulseradio unit relating to the athlete; displaying, at the central station,at least a portion of the information relating to the athlete; anddisplaying, at handheld units, an overlay of a field that indicates theposition and relative velocity of the athlete on the field.
 19. Themethod of claim 18, wherein the information relating to the athleteincludes a current position of the athlete on a field.
 20. The method ofclaim 18, further comprising the step of determining a position of theathlete using impulse radio technology.
 21. The method of claim 18,wherein the information relating to the athlete includes at least onemonitored vital sign of the athlete.
 22. The method of claim 21, whereinsaid step of displaying further includes indicating an alarm wheneverone of the at least one monitored vital signs exceeds a predeterminedthreshold.
 23. The method of claim 18, further comprising the step ofproviding a variety of sports related information to a user of ahandheld unit.
 24. The method of claim 23, wherein the sports relatedinformation includes statistics of the athlete.
 25. The method of claim18, further comprising the step of establishing secure communicationsbetween the athlete and a person using the central station or a handheldstation.
 26. A system comprising: an electronic device, attached to anathlete, including an impulse radio unit capable of transmitting animpulse radio signal containing information relating to the athlete; acentral station capable of obtaining the information and further capableof displaying at least a portion of the information relating to theathlete; and said central station is further capable of enabling anInternet site to display an overlay of a field and indicate the positionand relative velocity of the athlete on the field.
 27. The system ofclaim 26, further comprising a plurality of reference impulse radiounits distributed at known locations throughout the field.
 28. Thesystem of claim 27, wherein said central station is further capable ofdisplaying a current position of the athlete on the field that wasdetermined from the interaction between the impulse radio unit and atleast two of the reference impulse radio units.
 29. The system of claim26, wherein the information relating to the athlete includes at leastone monitored vital sign of the athlete.
 30. The system of claim 29,wherein said central station is further capable of displaying an alarmwhenever one of the at least one monitored vital signs exceeds apredetermined threshold.
 31. The system of claim 26, wherein saidcentral station or said electronic device is further capable ofestablishing secure communications between the athlete and a personusing the central station or a handheld unit.
 32. The system of claim26, wherein said athlete is a track and field athlete, a baseballplayer, a football player, a basketball player, a soccer player or ahockey player.
 33. An electronic device comprising: an interface unitattached to an athlete; an impulse radio unit, coupled to a centralstation, capable of enabling secure communications to occur between theathlete and another person; and said central station is further capableof enabling a television to display an overlay of a field that indicatesthe position and relative velocity of the athlete on the field.
 34. Theelectronic device of claim 33, wherein said impulse radio unit isoperable to interact with a plurality of reference impulse radio unitssuch that the central station can track the movement of the athlete. 35.The electronic device of claim 33, further comprising a sensor, coupledto said impulse radio unit, capable of monitoring at least one vitalsign of the athlete.
 36. A system for tracking at least piece of sportsequipment moving on a field, said system comprising: an impulse radiounit attached to each piece of sports equipment; a central stationcapable of receiving information related to a position of each piece ofsports equipment on the field; said central station is further capableof displaying an overlay of the field that indicates the position ofeach piece of sports equipment on the field; and said central station isfurther capable of enabling a television to display an overlay of thefield that indicates the position and relative velocity of each piece ofsports equipment on the field.
 37. The system of claim 36, wherein saidpiece of sports equipment is a football, baseball, soccer ball,basketball or hockey puck.
 38. A method for tracking at least one pieceof sports equipment moving on a field, said method comprising the stepsof: attaching, to each piece of sports equipment, an impulse radio unit;receiving, at a central station, information relating to a position ofeach piece of sports equipment on the field; displaying, at the centralstation, an overlay of the field that indicates the position of eachpiece of sports equipment on the field; and displaying, on a television,an overlay of the field that indicates the position and relativevelocity of each piece of sports equipment on the field.
 39. The methodof claim 38, wherein said piece of sports equipment is a football,baseball, soccer ball, basketball or hockey puck.